Electrodeposition with nickel



Patented Dec. 4, 1951 UNITED STATES PATENT orna e:

ELECTRODERO SITION': WITHiNICKEI; Etienne L. A. Ctmi'n,,New Yiirli, NI Y.,.vand' Siren E. Hybin'ette' and'Herbert B: 'l-ayl'or;Wilmimfi ton; Del., assignors; by m'esne assignmentefipto Kenmore--Metajls Gorporation, a corporation 01 Delaware NdDrawiiig, Applicationlime 26;.1946} Sbri'a'ITNO. 679,558

This invention relates tothe art of F electrode osition and is directed particularly-to a prceess= and to a" bath for the electrodepositiom nickel.

This application is a continuation-impart oi-i application'Serial N: 446x319; filed June-12; 1942,. now abandoned.

An object of this invention is to produce a: ductile nickel plating on metalwhich can be drawn; The ductility of-the product obtainable by the process of this: invention goesconsider ably beyond the previous standards -of ductility; inthis art. For example, at plated article:- is considered 1 ductile ii itcan be hammered or bent: without cracking; According t'o the -presentin vention, plated articles: may be made in whichthe product is so ductile that it may be drawn; several thousands of timesits: previous length and :the' drawn product can --still be bentgtwisted or braided-withoutcausingtheplating: tozcrack;

Another'object oi thisinvention is xto produc'e: aenickelplating bath from nickel or:nickel salts,-. hydrofluoric acid and a buffering. agent which? has substantially the same throwing power as asulphate-chloride type of nickelplating bath;

Another object 'of thiseinventionis to expedite: the rate of electrod'eposition; of. nickel andzat; the same :time: attain generally improvedioperati- 1 ing characteristics;

7 Another object 0f thisiinventiomis:toz produce a: bath which stays indefinitely in 1 condition 101': platingzwith' very." little; control. othenr than"; res plenishment 'yvithrwateiz and.;withiassmall amount: of fresh'lbathepreparemto; compensate Qifl: losses: by drag out.

Another; obj ect'zof: invention; is; to: produce ardepositiof nickelj.on.metal.:.with uniform :prop;-= erties throughout therentire: deposit.

Another; object. of: the presentinvention; is. to: produce; heavy deposits: of nickel on metal in; smooth condition; by; employing: a1 process and a bath .7 in. which the; nickel does. not i tree. as: heavily as in the priorart;

Theseandother objects ancillary theretovarei obtained by makingrup a bath ofIliCkeI, -11Y(1I0'-r fiuoric. acid and a-buffer= in which theeivarious. proportions of the; ingredients are? critical and in employing this bath to attain specified-con ditions set forth; below toproduce: the; smooth andior ductile: nickel deposit: or platmg'r,

Ingeneral 1 the: followinesproportions:and con+= ditiensiare: important the-practice :of: thiscim. vcntiomy L. The: amount. of: nickel: in the bath". should: beiat leastifio grams perzliter. Thmupperrlimit": oil" the nickel; content isz. determined; partly? by: the;temperatureremployed; the-higher -the temi-.- peratureethexlessrstablee or: seluble is' the nickel? saltt. Theaameunte of; nickeh. also? limited by the pH ofthe bath;,more'nickel beinesoluble aflf the lower pH valuesz Thus} the upper limit oi nickelcontent of the bath-is determined mainly by the solubility of the nickel' or" nickel: salt; Generally a hig-11' rii(:le1 content favors the pro duction' of a ductile plate at -high current dem sitiesa- With a low nickel content sueh as for example about iii-grams per liter, low currentdensities must be employed whichmight be une economical for commercial production How ever, asatiSfactoryplate may be obt'ained at ai slightly lower' nickel content.

2. The buffer employed in: the bath is: prefer? ably boric acid 'althoug-he it quite possible that other bufiers; such as the more ex-p'ensive citric acid or tartaric acid, could be employe'di-l The boric acid besidesacting: as a buffer: also reacts with the nickelion in the bathito:- producei Sis complex nickel; salt possibly a fluorob'orateit Thus; it is=preferable-toadd sonifiexcessgiof (the: boric acid over thatrequiredito react with?the: nickelin the-bath. The range ottliecb'oriczacids necessary-is from aboutl20 to oyeri'fifl (depending on the solubility- 1 grams per litera Thepresen'ce: of the bufier increases the stabilityroittheibathz 3; In making uptth'e: bath hydrogenrfluoride: is; preferably employed: a-l-thouglii .the addition: of a fiuoride' ion :irom' anotherrso'urce iiszsnot excludem, Apparently the:hydi'ofluoric:acidtereactsf-with the: nickel Land: :boric; acidgins the =bathzto-producerthe aiorementioned complex nickelaa salt. The by. drofluoric acid is employed excess -so. astm produce: the: desired pHZ which 18; on: the? acid side;

wezzhavez' also: found:.thatlthei boric acid content should :b'e-zrelatively; high" notiionlybyereasonof its ordinary buffer action?but becauseiit im proves anode corrosion,,lowers the tendency of heavy deposits to form trees}! and produces a more 1 ductile: deposit 4. The hydrogen ion concentration or pH of the bathi is important and generally must be maintained? between a pH 1 and a pH 6. Atthe pH'values oi close to 6 there is less tolerance permissible; on the other conditions.- maintained; in' the bath. Also at the h'igherpH, suchas about 6 orrab0ve, hydroxy1 inclusion in thepllat' ingma'y cause brittleness. The solubility oithe" nickel-or nickel salt in.:the bath increases as'th'e': pH value is'loweredf However, at around a pH 1} hydrogen inclusion in' the plating may cause brittleness. as: hydrogemj evolution is; increased at-.lower.:pH:values-.- Atzthevlower: pHl'va'lues one: obtains better: anode corrosion andixaismallert amount of bufferziscnecessaryx At therhigheitspfie values: the: ductility; ofi thezzproduct somewhat;

better.

5'. The: temperature of; the: bath: is; not? exr tremelyrcriticallbutzitiissnoted atatliesliigheni' temperatures theenickel salt tends to precipitate and at the lower temperatures the buffer or boric acid will tend to precipitate. Also the resistance of the bath decreases with increasing temperatures making a higher current density pos sible at the higher temperature; Although the nickel tends to precipitate at higher temperatures, with baths of low nickel content tempera- I tures of as high at 75 C. may be used. It is preferred, however, to operate at temperatures between 40 and 70 C.

6. The range of current density which can be employed is wide. It is well known that the more intensive the agitation of the solution and/or the' cathode, the higher is the current density which can be employed. Our invention enables us to employ current densities two to three times higher than generally is possible under the same conditions of agitation. (In the art, current density is always referred to the surface area of the cathode unless the anode is specified.) For the best ductility the current densities of from 3-50 amps. per square decimeter are advantageous. High current densities are known in one other type bath, i. e. the high chloride type bath. These baths have the disadvantages of having a very low pH and of being very corrosive and can only be used with special equipment and with special protection for the operation. For these reasons these baths have not gained wide popularity.

The baths of the present invention do not suffer from these defects.

It is also sometimes advisable to add a wetting agent to the bath which minimizes the effect of the evolution of hydrogen on the plate and, therefore, aids in the production of a more ductile and pore-free plate. Mechanical vibrations may also be employed to minimize the effect of the evolution of hydrogen. An example of a wetting agent which may be used is Duponol ME which is a fatty alcohol sulphate type of wetting agent. Other wetting agents of this type or of any type which will stand up in an acid solution with a high salt content may be employed. Examples of such wetting agents are: quaternary ammonium compounds such as lauryl pyradonium chloride, long chain polyethylene oxide compounds such as Carbowax, etc. I

Thefollowing examples of plating baths and operating conditions in addition to those given above (the acidic pH values resulting from the excess of hydrofluoric acid) will serve to further illustrate the invention:

Boric Current Tempera' Example Ni, in g./1. acid in density in ture. in pH g./l. amp./dm. degrees C 60 30 25 50 l 42 30 15 45 6.0 50 45 60 4 to 5 60 45 1 to 250 60 2. 5 to 4 48 45 120 60 4. 2 50 50 250 60 3.2 50 45 60 4 45 50 50 3. 5 1 to 12 60 4. 7 to 5. 2 36 40 1 to 15 60 4. 7 to 5. 2 75 35 1 to 250 4. 2 to 4. 7 15 to 25 5. 2

The examples with a pH of 1 produced somewhat brittle plates due to excessive evolution of hydrogen atthe cathode. Using a pH of 6, the main difliculty is the keeping of the nickel in solution. The examples with a pH of 6 and above produced somewhat brittle plate.

R It has been. determined that nickel deposited in accordance with the present invention is repreparatory plating. Among the various alloys on which we have plated nickel in accordance withthis invention is, for example, steel. The

plating of nickel directly on steel has always presented a difiicult problem, inasmuch as good adherence and freedom from pits have always been very difficult. to secure without special precautions, particularly when deposits greater than .0005" thick are required. It is common practice to first deposit copper on steel and then to deposit the nickel on the copper plating. However, by the use of the bath embodying the present invention no difiiculty is encountered in producing on steel a plating which possesses remarkable adherence and is substantially free from pits even when the thickness of the plating greatly exceeds .0005. Thus, according to the process of this invention, one plating step is eliminated and the results achieved are at least as good as those obtainable by the double plating processes of the prior art.

In the foregoing examples, ductility was also determined by making plates .002" thick on copper wire and bending the plated wire over a rod four times the diameter of the wire. The plate at the bend was dipped first in hydrochloric acid and then in sodium polysulphide, and then examined under a microscope. If no cracks were revealed there was considered to be a good ductile plate.

. A diameter steel wire plated according to Example 12 with 5% by weight of nickel and at a current density of 25-30 amperes per square decimeter was drawn from a length of 3 feet to 16,000 feet and in every stage of the drawing could be bent, flexed, twisted or otherwise worked. The drawn wire still contained 5% by weight of nickel as determined by chemical analysis. The resultant drawn wire was also more resistant to corrosion due to the fact that in the drawing process the nickel plating became denser and at the same time retained its continuity.

A 1" (outside diameter) brass tube plated with 10% by weight of nickel according to the process of Example 3 (above) with a current density of about 30 amps. per square decimeter was drawn to and the plating showed no signs of crackmg.

We believe that the degree of ductility achieved by the present invention is due to the crystal structure of the nickel deposit. X-ray tests seem to show that the nickel crystals deposited from our bath are not'deposited one alongside the other in the form known as trees but that a sufficient number of the crystals are aligned parallel to the surface of the base material to form brick-like layers and that these layers flow with the base metal when drawn, whereas a normal crystal growth perpendicular to the surface of the base metal separates when the plating is drawn.

The tendency of nickel to become passive when employed in an electroplating anode is well known and is highly objectionable in that it commonly causes the nickel anode to corrode unevenly and in that it prompts the undue release from the anode of metallic particles. These particles, aside from'representing a loss of nickel, often fall on the work being plated and cause blemishes in the plate. By the use of specially compounded and treated anodes, uneven corrosion of the anode and the undue release of metallic particles therea, were Inasmuch as the bath embodying the present l invention contains an excess of hydrofluoric acid, it becomes necessary to employ tanks or vessels which are resistant to this acid. Vitreous tanks and; wood vessels should be avoided, but hard rubber or rubber coated steel may be used to advantage; Vitreous tanks, however, are usable with a high pH.

Nickel plating baths in common usage cannot hold-much iron in solution with the result that if any appreciable amount of iron is introduced it will be precipitated. Most nickel anodes contain some iron which enters the solution continuously, only to be precipitated. It has heretofore often been found necessary to constantly filter the solution or provide a very deep electroplating tank so that the iron precipitate may settle to such a depth in the bath as to obviate the danger of its being stirred up during the carrying out of the plating process. By use of my improved electroplating bath, all iron entering into the solution from the anode (assumingthe anode is primarily nickel and contains some iron). will remain in solution, thus obviating the formation of an iron precipitate. During the course of the electroplating operation, the iron in solution will be plated out with the nickel and deposited on the cathode. Thus, it will be understood that iron may, by design, be added to the solution for the purpose of producing a plate consisting of a nickel iron alloy. In such a case, certain of the anodes would be constituted of iron. Likewise, the bath is such in its operation that cobalt may be intentionally introduced in the solution when an electrodeposition of cobalt is desired along with the nickel.

vSeveral courses are available for the preparation of the bath. It can be prepared, for example, by dissolving solid commercial nickel carbonate in hydrofluoric acid or by electrolyzing hydrofluoric acid with nickel anodes. While in theclaims reference is made v to the nickel being present in the form of nickel fluoride, it will be understood that actually nickel will be present, largely in the form of complex salts includingnickel fluoborates. Accordingly, it is contemplated that the term nickel fluoride embraces complex nickel salts. The plating bath should be as pure as possible for high current densities. Thus, traces of lead if over .04 per cent which might enter the hydrofluoric acid from a lead container may lead to brittleness, flaking and bad appearance in general.

By the addition of known brightening agents such as, for example, a mixture of paratoluene sulfonamide, saccharine and fuchsin the baths of the present invention may beemployed for producing bright plating and it is then possible to work with high current densities (up to 2 or more) compared to the commercial brightening baths. This possibility of working with high current densities is the important advantage in baths of the present invention where brightening agents are added since it is well known in the art that the addition of brightening agents to the electroplating baths reduces the ductility of the plating.

The particular bath employed when plating ac cordingto the present invention depends upon such factors as the ductility required, the rate of deposition required, and the character of the plating operations to be undertaken. The exact composition of the bath and the operating characteristics thereof for any particular set of requirements will be apparent to those skilled in theart.

We claim:

1. A method for producing a relatively ductile nickel plating on a metal base which comprises passing a current of less than 250 amperes per square decimeterfrom a nickel anode to themetal base to be plated through a bath formed essentially from a nickel compound, hydrofluoric acid, boric acid and water, said hydrofluoric acid reacting with said nickel compound to form a.

complex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel compound to said complex nickel fluoride, said bath containing at least 30 grams or" nickel metal per liter, said excess hydrofluoric acid giving said bath a pH of f more than 1 and less than 6, the anions of said bath comprising essentially fluorides and borates.

2. A method for producing a highly ductile nickel plating on a metal base which comprises passing a current of less than 250 amper S per square decimeter from a nickel anode to the metal base to be plated through a bath formed essentially from nickel carbonate, hydrofluoric acid, boric acid and water, said hydrofluoric acid reacting with said nickel carbonate to form a com plex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel carbonate to said complex nickel fluoride, said bath containing at least 30 grains of nickel metal per liter, said excess hydrofluoric acid giving said bath a pH of more than 1 and less than 6, the anions of said bath comprisin-g essentially fluorides and. borates.

3. A method for producing a highly ductile nickel plating on a metal base which comprises passing a current of less than 250 amperes per square deoimeter from a nickel anode to the metal base to be plated through a bath formed essentially from nickel, hydrofluoric acid, boric acid and water, said hydrofluoric acid reacting with said nickel to form a complex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel to said complex nickel fluoride, said bath contain ing at least 30 grams of nickel metal per liter, said excess hydrofluoric acid giving said bath a pH of more than 1 and less than 6, the anions of said bath comprising essentially fluorides and borates.

4. A method for producing a highly ductile nickel plating on a metal base which comprises passing a current of less than 250 ampcres per square decimeter from a nickel anode to the metal base tobe plated through a bath formed essentially from a nickel compound, hydrofluoric acid, boric acid and water, said hydrofluoric acid reacting with said nickel compound to form a complex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel compound to said complex nickel fluoride, said bath containing at least 30 grams of nickel metal per liter, and 20 60 grams of boric acid per liter, said excess of hydrofluoricacid giving said. bath a pH of more than 1 and less than 6-, the anions of said bath comprising essentially fluorides and borates. '5. A method for producing a highly ductile nickel plating on a metal base which comprises passing a current of less than 250 amperes per square decimeter from a nickel anode to the metal base to be plated through a bath formed essentially from a nickel compound, hydrofluoric acid, boric acid and water, said hydrofluoric acid reacting with said nickel compound to form a complex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel compound to said complex nickel fluoride, said bath containing from 42 to 60 grams of nickel metal per liter, said excess hydrofluoric acid giving said bath a pH of more than 1 and less than 6, the anions of said bath comprising essentially fluorides and borates.

6. A method for producing a highly ductile nickel plating on a metal base which comprises passing a current of from to less than 250 amperes per square decimeter from a nickel anode to the metal base to be plated through a bath formed essentially from a nickel compound, hydrofluoric acid, boric acid and water, said hydrofluoric acid reacting with said nickel compound to form a complex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel compound to said complex nickel fluoride, said bath containing at least grams of nickel metal per liter, said excess hydrofluoric acid giving said bath a pH of more than 1 and less than 6, the anions of said bath compris- I ing essentially fluorides and borates.

'7. A method for producing a highly ductile nickel plating on a metal base which comprises passing a current of from 15 to less than 250 amperes per square decimeter from a nickel an ode to the metal base to be plated through a bath formed essentially from a nickel compound, hydrofluoric acid, boric acid and water, said hydrofluoric acid reacting with said nickel compound to form a complex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel compound to said complex nickel fluoride, said bath containing from 42 to 60 grams of nickel metal per liter, said excess hydrofluoric acid giving said bath a pH of more than 1 and less than 6, the anions of said bath comprising essentially fluorides and borates. I

8. A bath for the electrodepositicn of a relatively ductile nickel coating on a metal base which is formed essentially from a nickel compound, hydrofluoric acid, boric acid and water, said hydrofluoric acid reacting with said nickel compound to form a complex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel compound to said complex nickel fluoride, said bath containing at least 30 grams of nickel metal per liter, said excess of hydrofluoric acid giving said bath a pH of more than 1 and less than 6, the anions of said bath comprising essentially fluorides and borates, said bath producing said relatively ductile nickel coating when operated at current densities of less than 250 amperes per square decimeter.

9. A bath for the electrodepositicn of a highly ductile nickel coating on a metal base which is formed essentially from nickel carbonate, hydrofluoric acid, boric acid and water, said hydrofluoric acid reacting with said nickel carbonate to form a complex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel carbonate to said complex nickel fluoride, said bath containing at least 30 grams of nickel metal per liter, said excess hydrofluoric acid giving said bath a pH of more than 1 and less than 6,, the anions of said bath comprising essentially fluorides and borates, said bath producing said highly ductile nickel coating when operated at current densities of less than 250 amperes per square decimeter.

10. A bath for the electrodepositicn of a highly ductile nickel coating on a metal base which is formed essentially from nickel, hydrofluoric acid, boric acid and water, said hydrofluoric acid reacting with said nickel to form a complex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel to said complex nickel fluoride, said bath containing at least 30 grams of nickel metal per liter, said excess hydrofluoric acid giving said bath a pH of more than 1 and less than 6, the anions of said bath comprising essentially fluorides and borates, said bath producing said highly ductile nickel coating ductile nickel coating on a metal base which is formed essentially from a nickel compound, hydrofluoric acid, boric acid and Water, said hydrofluoric acid reacting with said nickel compound to form a complex nickel fluoride, said hydrofluoric acid being present in a quantity in excess of that required to convert said nickel compound to said complex nickel fluoride, said bath containing at least 30 grams of nickel metal per liter, and 20-60 grams of boric acid per liter, said excess of hydrofluoric acid giving said bath a pH of more than 1 and less than 6, the anions of said bath comprising essentially fluorides and borates, said bath producing said highly ductile nickel coating when operated at current densities of less than 250 amperes per square decimeter.

12. A bath for the electrodeposition of a highly ductile nickel coating on a metal base which is formed essentially from a nickel compound,

hydrofluoric acid, boric acid and water, said hy-- drofluoric acid reacting with said nickel compound to form a complex nickel fluoride, said' hydrofluoric acid being present in a quantity in excess of that required to convert said nickel compound to said complex nickel fluoride, said bath containing from 42 to grams of nickel metal per liter, said excess hydrofluoric acidgiving said bath a pH of more than 1 and less than 6, the anions of said bath comprising essentially fluorides and borates, said bath producing said highly ductile nickel coating when operated at current densities of less than 250 amperes per square decimeter.

Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Loose Mar. 16, 1943 OTHER REFERENCES Transactions of the American Electrochemical Society, vol. 15 (1909), pages 464, 465; vol. 23

Number (1913), pages 145, 146, 147; vol. 39 (1921), pages 460-481; vol. 81 (1942), pages 2137-229. 

1. A METHOD FOR PRODUCING A RELATIVELY DUCTILE NICKEL PLATING ON A METAL BASE WHICH COMPRISES PASSING A CURRENT OF LESS THAN 250 AMPERES PER SQUARE DECIMETER FROM A NICKEL ANODE TO THE METAL ALSO TO BE PLATED THROUGH A BATH FORMED ESSENTIALLY FROM A NICKEL COMPOUND, HYDROFLUORIC ACID, BORIC ACID AND WATER, SAID HYDROFLUORIC ACID REACTING WITH SAID NICKEL COMPOUND TO FORM A COMPLEX NICKEL FLUORIDE, SAID HYDROFLUORIC ACID BEING PRESENT IN QUANTITY IN EXCESS OF THAT REQUIRED TO CONVERT SAID NICKEL COMPOUND TO SAID COMPLEX NICKEL FLUORIDE, SAID BATH CONTAINING AT LEAST 30 GRAMS OF NICKEL METAL PER LITER, SAID ESCESS HYDROFLUORIC ACID GIVING SAID BATH A PH OF MORE THAN 1 AND LESS THAN 6, THE ANIONS OF SAID BATH COMPRISING ESSENTIALLY FLUORIDES AND BORATES. 